Carbons which are capable of functioning as catalysts per se are well known. For example, as early as 1867 Calvert observed that the presence of charcoal enhanced a variety of oxidation reactions, including the oxidation of hydrogen sulfide, phosphine, and various organics. In those instances where carbon has been observed to affect such reactions, it has functioned as a true catalyst, i.e. it affects only the rate of a given reaction but is not itself changed by the reaction to any significant degree. It is also known that carbon chars prepared from nitrogen-rich starting materials are much more effective in catalyzing certain reactions than those prepared from nitrogen-poor feedstocks. Also, enhanced catalytic properties can be imparted to high-temperature chars prepared from nitrogen-poor starting materials by simply exposing such chars to nitrogen-containing compounds such as ammonia at high temperatures. High-temperature chars are those prepared at temperatures greater than 700.degree. C. while low-temperature chars are prepared at temperatures less than 700.degree. C. A number of investigators have prepared catalytically-active chars by the simple calcination or calcination-activation of low- or high-temperature chars prepared from nitrogen-rich materials such as polyacylonitrile and polyamide.
More recently, the oxidation of high-temperature chars prepared from nitrogen-poor feedstocks prior to or during exposure to nitrogen-containing compounds has been explored. Similarly, the oxidation of a low-temperature char prepared from nitrogen-rich feedstocks such as polyacrylonitrile has been evaluated.
However, all of the prior art processes for preparing carbons which are catalytically active per se have certain disadvantages which limit their overall utility and practicality. For example, some use nitrogen-rich starting materials such as polyacrylonitrile or polyamide. Such materials are expensive and have been found to generate large amounts of cyanide and other toxic gases upon carbonization. Those that use chars derived from nitrogen-poor starting materials invariably also use high-temperature chars, such as activated carbons, which require further processing. Since such materials are fairly inert chemically, the use of extensive and aggressive chemical post-treatments is usually required to effect significant changes in their catalytic capabilities. The use of high-temperature chars is, therefore, inevitably more expensive than the direct use of the raw materials from which they are derived. Additionally, such processes involve the use of large amounts of toxic and/or hazardous reagents such as nitric acid, sulfuric acid, ammonia, or toluene diisocyanate, and the generation of significant amounts of toxic and/or hazardous byproducts such as sulfur dioxide, nitric oxide, and cyanide.
Accordingly, it is the object of the present invention to provide an improved process for the manufacture of a catalytically-active carbon wherein the carbon catalyst is is prepared directly from an inexpensive and abundant nitrogen-poor starting material such as a bituminous coal or a bituminous material. It is further the object of the present invention to limit the use of agents responsible for imparting catalytic activity to the carbon by performing the essential treatments during the low temperature transition of the starting material to the final product. These treatments include oxidation of the low temperature char, preferably by inexpensive, abundant, and relatively non-toxic oxidants. The oxidized, low-temperature char is then contacted with small amounts of an inexpensive, abundant, and relatively non-toxic nitrogen-containing compound in combination with sucrose or fructose prior to and/or during the initial exposure of the oxidized char to temperatures greater than 700.degree. C. By this method, carbon materials with high catalytic activity per se for a variety of chemical reactions can be manufactured relatively inexpensively and conveniently, with minimal departure from conventional processes for the manufacture of high-temperature carbon chars such as activated carbons and coke.